Sara, you've got some fantastic advice from everyone here which I can only second.
The only thing I have to add is to say that you're only this age once and you're the one that needs to enjoy it. In no time you'll be in your twenties and then thirties - it just goes so very fast that if you wait till you've lost your weight to get out there and enjoy yourself, you're going to look back and regret not doing that.
I know it's not easy, but forget about those other people! Why are the opinions of strangers, who you'll never see again in all likelyhood, that important to you? They're not. If they have an issue with a fat chick going out there and having fun, they're the ones with the problem - not you!
Next time that band comes to town, I hope you'll go - no matter what weight you are.
And I also want to be like Tracey when I grow up. Or Robin. Or Laurie. Or Rhonda. Or Lisa. Or before I name every single person on the forum, anyone who's not let themselves give in to the self consciousness and made a success of this.